Canines that resorb lateral incisors – can it be a Win-Win situation?

Published: January 2013

Bulletin #18 January 2013

Canines that resorb lateral incisors – can it be

a Win-Win situation?

The cause-and-effect relation between incisor root
resorption and an adjacent impacted canine is well known, although an accurate
assessment of its prevalence in the population at large, was not established
until very recently. The first recorded investigation in the literature was
published in 1978, when Kurol and associates found a 12% prevalence among
Swedish schoolchildren using plane film radiography.1 However, as they pointed
out in their article, because plane film radiography cannot provide imaging of
the bucco-lingual surfaces of the incisors, the actual occurrence of resorption
was probably considerably higher and that it largely went undiagnosed.

With the advent of computerized tomography and its ability
to image in the bucco-lingual plane, the same group of researchers repeated the
study, using a regular hospital spiral CT machine. They found that nearly half
the cases of canine impaction within their sample exhibited incisor root
resorption2. In a further update using cone-beam “dental” CT equipment, the
group of James Mah in Southern California was able to detect incisor root
resorption in almost two thirds of the cases3.

Without doubt, most of the cases
were only mildly affected, but a year or two before the CT scan, it must be
assumed that there was no resorption and that a year or two in the future could
conceivably have seen the resorption much more advanced. It might not reach the level of inevitability of
being “only a little pregnant” but, without appropriate treatment, the prognosis
of the affected tooth must surely be compromised.

So, the question is: “what is appropriate treatment and can
we offer a reliable degree of hope that the resorption will stop, that the affected
incisor can be moved to its place, that it will last for many years hence and
that the canine can be brought into the dental arch?”

In general, the “collision course” eruption path of the
errant canine is at an angle to the orientation of the long axis of the incisor
root. This being so, one can imagine that the canine will reach a certain location
on the root surface of the incisor and that the resulting resorption process
will follow the general line of the canine’s path, to produce an oblique lacuna
or gouged out loss of integrity in the continuity of the incisor root surface.
A minor “side-swipe” may produce little damage and the canine may then continue
on along its eruptive path, possibly to erupt unaided. On the other hand, it
may hit the middle of the incisor root and cause more devastating root loss.
When the location of the canine is higher, more mesially situated and with a
more vertical orientation, it may cause severe root destruction, leading to a
shedding of the incisor. So, despite the fact that case reports have been
published in its support, the “no treatment” option is a risky business and
should be weighed very carefully, having full knowledge of the location and
eruption path of the canine – for which a CBCT examination is essential.

In 2005, we published a study of a
cohort of patients with severely resorbed maxillary incisors from this cause,4 which clearly showed that the progress of the resorptive
process halts when the canine is distanced from the area. It also showed that
the prognosis of the affected teeth was very much improved following thetreatment, none were lost
during the treatment and in the (often many) years that they were followed up,
despite their extremely short roots and despite the fact that they had also been
subjected to orthodontic movement, as an integral part of the overall treatment.

Impacted canine patients are typically class 1 cases with
little or no crowding and are seldom cases in which the orthodontist would want
to extract teeth as part of their treatment. For this reason, extraction of the
affected incisor or of the canine offers the specter of replacement by an
implant when the patient reaches adulthood, with some form of temporary
restoration in the meantime. Alternatively, the practitioner may elect to
substitute posterior teeth for the extracted incisor or canine, by drawing
these teeth mesially into a class 2 occlusal relationship, while trying to
avoid adverse changes in the dental midline and in the overjet – an exercise
that few of us can approach with the aplomb of one or two of our outstanding
colleagues. For these reasons, therefore, achieving a satisfactory result that
includes alignment of both canine and incisor with a good long term prognosis
has important advantages.

Case Report

The case presented here is of a female patient aged 10.9
years, referred by an orthodontist who considered that the resorbed lateral
incisor, due to an impacted canine, should be extracted. The parents requested
a second opinion.

Fig. 1. The intra-oral views of the 10.9 year old female patient,
showing the over-retained deciduous left canine, the peg-shaped lateral
incisors and the crossbite relationship of the left lateral incisor.

Clinical examination

The lips were incompetent and there was an open mouth
posture at rest, with an everted lower lip. The child featured a mild skeletal
class 3 profile with a minor degree of facial asymmetry. The maxillary midline
was coincident with the facial midline, while the mandibular midline was 2-3mms
to the left side. There was a loose, over-retained maxillary left deciduous
canine, but aside from that, the dentition was fully erupted, including
mandibular second molars. The maxillary left lateral incisor and the deciduous
canine were in crossbite, but there was no premature contact on these teeth,
nor was there a functional deviation into centric occlusion. The mandibular
dentition was well aligned. The left side premolar/molar relations were ideally
intercuspated in a solid class 1 relation, while the right side was almost a ½
unit class 3.The maxillary lateral
incisors were frankly peg-shaped. The left lateral incisor exhibited a
considerable degree of mobility (Fig. 1).

Radiographic examination

Fig. 2. Periapical and panoramicviews showing the impacted canine and associated severely resorbed
lateral incisor. Note also the apparently arrested root development of several
other teeth with open root apices and the absence of third molars.

The panoramic radiograph showed all teeth present except
third molars and the maxillary second molars were unerupted. The left maxillary
canine was seen to be impacted and pointing in the direction of the adjacent
lateral incisor, whose root was severely resorbed with less than half
remaining. The orientation of the long axis of this incisor exhibited a
mesio-angular tip. The root of the deciduous canine was completely resorbed. The
panoramic and the periapical views of this tooth depicted the relation of the
crown tip of the canine to the resorption front of the incisor root, with no
apparent superimposition (Fig. 2). Given the widely different angle between the
central ray of the panoramic film to that of the periapical film and the
“tube-shift” diagnostic parallax views that it offered, it was concluded that
the canine could only be directly in line with the incisor or only very
marginally buccal or lingual to its root.

Fig. 3a. Axial (horizontal) cuts from the CBCT at 3 different
levels, which show the resorption of the root of the lateral incisor and a large
void of bone destruction surrounding it.

Fig. 3b. Transaxial (vertical) cut shows the degree of root
resorption of the incisor and the cusp tip of the canine above it. The void of
bone destruction associated with the resorption process is in evidence.

Fig. 3c. A Youtube video clip of this patients CBCT is available at http://youtu.be/I2EU_U4CWDM which presents the 3D image of the immediate area and gives
an excellent depiction of the location and relationships of the canine with the
surround structures including the anatomy of the root resorption/soft tissue interface.

In order to decide whether to expose the tooth from the
buccal or palatal side and whether the canine should be drawn labial or palatally
away from the incisor root, a CBCT was considered essential if surgical and,
later, orthodontic damage was to be minimized or, hopefully, avoided (Fig.
3a,b). The 3-D views and video clip (Fig. 3c) indicated that the canine nestled
in a resorption crater which was bucco-lingually longer on the palatal side
than on the labial. Logically, therefore, it was determined that the tooth had
to be exposed and traction applied on the labial side.

Biomechanics I

Given the degree of resorption present, there was
considerable urgency to expose the tooth which, in these unusual circumstances
generally dictates that this be done even before leveling and alignment and
space has been made in the arch. However, anchorage to resist the future
traction force needed to be provided, with a fully bonded appliance set-up and,
since it was possible to achieve all these aims very quickly in this case, leveling
and alignment were undertaken before the surgery.

Fig. 4. The Tip-Edge Plus appliance was placed in January 2012,
with no bracket placed on the affected lateral incisor and the deciduous
canine.

A maxillary Tip-Edge Plus appliance (Fig. 4) was applied to
all the erupted teeth except the lateral incisor and the deciduous canine of
the left side and 8 weeks passed between 4 January 2012 and 1 March 2012,
before a heavy stainless steel main arch (0.020” round) could be placed. At
this point the patient was referred to the surgeon.

Surgery

Fig. 5. On 1 March 2012, following the achievement of leveling and
alignment and immediately prior to surgery, a heavy 0.020” steel main arch was
placed, with an auxiliary arch of 0.016” stainless steel ligated over it, in
“piggy-back” style. The auxiliary arch carried a long loop opposite the canine
area, with a terminal helix which, in its passive mode, protruded horizontally
outward.

Immediately prior to surgery, a labial 0.016” stainless
steel auxiliary archwire, fashioned to include a long horizontal loop was
placed in the brackets, which was designed to move the canine labially away
from the lateral incisor root apex (Fig. 5).

Fig. 6a. At surgery, the deciduous canine was extracted and the permanent
canine exposed with a full labial flap taken from the crest of the ridge. Only
the middle of the canine crown on its labial side was exposed, care taken not
to approach the tip of the crown because of its proximity to the resorbed apex
of the lateral incisor. Although the extraction of the deciduous canine had
exposed the interproximal bone adjacent to the root of the lateral incisor, the
incisor itself was undisturbed (Surgery by Prof. Raffi Zeltser).

Fig. 6b. A small eyelet was bonded to the canine, as close to the
tip as was possible, with a twisted soft steel ligature threaded through it and
twisted tightly.

Fig. 6c. The long horizontal loop of the auxiliary archwire was
raised with light finger pressure and ensnared in the twisted ligature which
had been shortened and turned into a small hook.

Fig. 6d. The full flap was re-sutured under the loop, to cover the
exposed canine and the distal side of the incisor, leaving only the hooked end
of the twisted ligature visible.

Under local anesthetic cover, the
surgeon then exposed the labial and distal aspects of the canine using a labial
muco-gingival flap, taking care not to expose the cuspal tip of the canine,
which was in close proximity of the resorption front of the incisor (Fig. 6a).An eyelet attachment was bonded to the labial
side of the canine crown (Fig. 6b) and the entire labial flap resutured to it
former place, to re-cover the tooth. The twisted pigtail ligature that was tied
into the eyelet was brought horizontally through the flap and fashioned into a
hook, close to the mucosa (Fig. 6c).

The loop of the auxiliary stainless steel archwire was
pressed upwards into the sulcus area, under light finger pressure, and engaged by
the hooked end of the twisted pigtail ligature as close as possible to the
mucosa covering the alveolus opposite the exposed and now re-covered tooth. A
labially-directed force was thus effective immediately and before the patient
had left the surgeon operatory (Fig. 6d).

Biomechanics II

Fig. 7. The rapidity of the initial movement is seen in these
views, taken 12 days post-surgery and is almost certainly due to the resorption
void that surrounds the canine crown. As may be seen, once the canine is
palpably clear of the incisor root, the direction of traction is altered by
drawing the tooth distally towards the premolar.

The patient was seen by the surgeon a week later for the
removal of the sutures and by the orthodontist just 12 days post-operatively.
At this visit, it was noted that the canine had become extremely obvious,
bulging and clearly about to break through the oral mucosa (Fig. 7). The
auxiliary archwire was discarded and elastic thread was drawn between the
pigtail ligature and the interbracket span between the two premolars. The aim
of this alteration in traction direction was to apply a distal force towards
the tooth’s place in the arch and, hopefully, still beneath the oral mucosa (Fig.
7).

Surgery II

Fig. 8. In April 2012 and after 5 weeks of distal movement, it had
been planned to perform an apically repositioned gingival flap, in orderto place crestal attached gingiva over the crown
of the canine. Unfortunately, the canine had already broken through the oral
mucosa, high in the sulcus. The eyelet was removed and an orthodontic bracket
substituted to complete the alignment, at the same time as a similar bracket
was placed on the lateral incisor. Note the use of 2 different Nickel/Titanium
archwires. The 0.014” main arch was ligated in the bracket slots and applied
eruptive force to the canine, while a 0.012” auxiliary arch was threaded
through the deep channel in the Tip-Edge Plus bracket, to engage the lateral
incisor.

The plan was to perform a secondary surgical procedure to
raise and apically reposition an attached gingival flap when the tooth had
reached its predetermined buccal location, still high in the sulcus, before
completing the orthodontic treatment. Unfortunately, the tooth broke through
the oral mucosa during this distal traction and the opportunity was lost (Fig.
8).

Biomechanics III

When the tooth had reached a point vertically above its
intended location, the eyelet was substituted by a Tip-Edge bracket and, with
the lateral incisor now unencumbered by the presence of the canine, a similar
bracket was place on it, despite its severely resorbed root and its high degree
of mobility. Using an 0.012” NiTi wire threaded through the horizontal deep
channels of the Tip-Edge bracket from second premolar to second premolar, via
the lateral incisor bracket and a similar 0.014” Niti archwire ligated into the
regular slots and engaging the canine, two separate and parallel systems were
created using the full upper dentition as anchorage. Because orthodontic
alignment in the mandibular arch required very little time, brackets were only
bonded at this late juncture, on 28 May 2012.

Active treatment was completed on 19 September 2012 and the
appliances left in place and in a completely passive mode for a further three
weeks. No attempt was made to correct the mild class 3 occlusion of the right
side of the mouth, since this would have involved a very considerable extension
of treatment duration and much reactive force to resist the needed and desirable
movement of the maxillary right posterior teeth. This would have potentially
and unnecessarily detracted from the well-being of the anterior teeth in
general and the lateral incisor in particular. Success in saving both the
lateral incisor and the canine was not inconsiderable and, as such, was not to
be undermined by lesser considerations.

Figs. 9 & 10. In October 2012, the alignment of the teeth was
completed, including the correction of the crossbite of the lateral incisor and
the uprighting of its root. The appliances were removed and the patient provided
with removable Hawley retainers. It will be noted that minor discrepancies in
the occlusal relations still remain in what may be described as an optimal
(rather than ideal) result, given the need to avoid unnecessary movements that
could undermine the prognosis of the resorbed lateral incisor.

Fig. 11. A close-up view of the gingival condition around the
lateral incisor and canine on the day appliances were removed. Note the normal
clinical crown height in relation to the adjacent teeth. The labial side of the
canine is covered with non-keratinized epithelium, which may require
periodontal modification, after a period of “settling down”. Mobility of the
lateral incisor was markedly reduced and only marginally greater than that of
the other incisors.

Debonding was performed on 10 October 2012 (Figs. 9-11),
with extreme care being exercised in relation to the lateral incisor. Retainers
were placed and, when last seen on 7 November 2012, the retainers were
prescribed for night-time use only. An examination of the lateral incisor
revealed that this tooth had become much firmer and, while still with slightly greater
mobility than the other teeth, it had tightened up very significantly. Eventually,
laminate restorations will be considered for the patient and are planned for
several years hence – at a time when it is fully expected that the lateral
incisor will be firm, despite its short root. Well trabeculated bone support can
be seen in the post-treatment radiographs (Fig. 12) and its further maturation should
eliminate the remaining mobility within a few months and splinting will not be
necessary from the periodontal point of view, although it might be a
consideration for the long term retention of the orthodontic alignment.

Fig. 12. Periapical and panoramic views, taken immediately
following debonding, show that the resorptive process has come to a complete
halt with no measurable change in the root length of the incisor. Bony
trabeculation is seen in the previous resorption void and this fill-in is
expected to mature further in the next few months.

Further follow-up of the longevity of this case will be made
and the present January 2012 bulletin will be updated from time to time with
the inclusion of new radiographs to show the condition of the bone support of
this tooth in the medium and long term.

Discussion

Perhaps the most important contribution to come out of the
study4 that was performed in Jerusalem in 2005 was that the severe
resorption of incisor roots by an aberrant canine will be arrested as soon as
the impacted tooth is distanced from the immediate area of the root apex. To
date, 7 years after publication of that article, the affected teeth in the cases
that comprised the investigative sample in that clinical research study, are
still in place, firm and without further root loss. Hence the confidence that
is offered in publishing this case, not as a sensational “one-off” success, but
rather as a modus operandi in these cases, in general.

The second point worth noting is that almost half the cases
of palatally impacted canines are associated with anomalous lateral incisors,
i.e. missing, peg-shaped and small. Nevertheless, it has been shown that
associated resorption of the lateral incisors occurs far more frequently in the
cases with normal lateral incisors than those with lateral incisors of reduced
dimensions.5 The present case is unusual in this respect.

Mobility of the resorbed lateral incisor at the outset will
convince most orthodontists that the tooth has a poor prognosis, will surely be
lost within a short period of time and that it would be unwise to include it in
the long term plan for the dentition as a whole, particularly if it requires to
be moved orthodontically. Without question much of the mobility must be linked
to the shortness of the root.

However, when reviewing these cases, the pre-treatment
radiographs will show a very wide radiolucent area around the crown of the
canine and the resorption front of the incisor, with a complete absence of
bone. When treatment is completed, the immediate post-treatment periapical
radiographs will show new bone filling in the former void and, within a few months,
the lattice work of bony trabeculation, which contributes to the rejuvenated
support that will significantly reduce the mobility. We have found that
splinting to provide physical support for the teeth in all but the most extreme
cases, is unnecessary – although it may be a useful adjunct for retention of
the orthodontic alignment.

Since this type of root resorption is very aggressive, it is
essential that exposure, bonding and distancing of the canine be undertaken
within a very short time of the diagnosis being made. In general it is
advisable that it be done even before the more usual treatment sequence of leveling
and alignment is undertaken. However, in the present case, the classic protocol
with this preliminary orthodontic phase was considered to be justified because
it needed to be of very short duration. However, the lateral incisor was not
bracketed initially, in order that there should be no possibility of aggravated
root resorption as the result of orthodontic movement of the incisor root
against the impacted tooth.

Were the surgeon to carry out an open exposure, there would
be no possibility of achieving an opening which may be expected to remain
patent in the post-surgical weeks and months, without seriously endangering the
vitality of the incisor and likely threatening the success of the entire
undertaking. A closed eruption exposure is the only way in which all the aims
of the plan may be achieved6-8.

Ideally and from the periodontal point of view, the
orthodontist would want to draw the canine inferiorly and to erupt it through
attached gingiva which, because of its relation to the incisor root, is
mechanically impossible. The canine must be first drawn labially away from the
incisor root apex and towards the oral mucosa. Once it has become palpable,
bulging the mucosa on the alveolar side of the sulcus, above its place in the
arch, the ideal procedure to perform is the apically repositioned flap which is
aimed at suturing attached gingiva on the crown of the tooth while it is being
drawn into its place.

Given that the area around the crown of the canine is devoid
of bone, any labially directed force will move the tooth very rapidly indeed
and, as in this case, the opportunity to perform the apical repositioning
procedure may be easily missed. The result will be that the tooth will be
invested in oral mucosa on the labial side, which will probably require minor
periodontal surgery at a later date, once orthodontic treatment is completed.

A word of caution is appropriate in the present context in
regard to the orthodontic movement of these resorbed teeth. While we have
asserted that further root resorption is most unlikely to occur once the canine
is distanced from the area and that these teeth can be subsequently moved
orthodontically, we would recommend that the orthodontic treatment should be
kept to the minimum that is absolutely necessary. We would warn against large
scale orthodontic movements and, as in the case described here, being prepared
to accept reasonable compromises for an optimal result. It should be remembered
that the antithesis of accepting the “good” may be the striving for
“excellence”.

Postscript

At the 15 month post-treatment follow-up visit, the condition is most satisfactory, with virtually no mobility of the resorbed incisor. The periapical radiograph taken on that day shows excellent mature bony trabeculation and a normal lamina dura, as predicted.